Seed production of Pappophorum subbulbosum in rangelands of Southwestern Buenos Aires

TORRES, Y.A., C.A. BUSSO, O.A. MONTENEGRO, H.D. GIORGETTI, G.D. RODRÍGUEZ, T. MONTANI AND A. MAIDANA

Tafí del Valle, Tucumán

Jornada; XXIV Jornadas Científicas de la Asociación de Biología de Tucumán; 2007

Sociedad de Biología de Tucumán

Persistence of native species within a community depends upon, at least partially, of natural reseeding which is determined by seed production. Perennial grasses exposed to grazing vary in their sensitivity to forage removal. However, most of them have a rapid recovery if defoliation is early enough as to allow time for complete seed maturation. Pappophorum subbulbosum is among the native, warm-season, high forage value perennial grass species in southwestern Buenos Aires. However, and despite the importance of this rangeland species, a clear knowledge of its seed production and response to early defoliation does not exist. The objective of this study was to quantify seed production in P. subbulbosum. Studies were conducted between October 2006 and May 2007 in the Chacra Experimental de Patagones (40º 39´S, 62º 54´W; 40 m.a.s.l.), within the Phytogeographical Province of the Monte. Two-year-old plants obtained from seeds and established at the field were used in this research. At the end of November and mid-December 2006, a defoliation treatment was applied to half of the plants leaving 5 cm stubble. Apical meristems were not removed by the defoliation event because them were at 5.8 ± 0.9 mm height. The other half of the plants remained undefoliated (controls). Every 21 days during the whole growing season, the number of reproductive tillers/plant was determined. Seeds were harvested and quantified at the time of their dispersal. Data were analyzed using one-way ANOVA. When F tests were significant (p<0.05), LSD test was used for mean comparisons. The greatest (p<0.05) number of reproductive tillers/plant was observed during December  2006 (17.5 ± 4.5 for control plants and 12.1 ± 1.4 for defoliated ones). Seed number/reproductive tiller was similar (p>0.05) between treatments (26.1 ± 6.6 for controls and 23.2 ± 3.9 for defoliated plants). Seed number/plant was also similar (p>0.05) between treatments (304.6 ± 122.7 for control plants and 192.1 ± 45.0 for defoliated ones). The number of reproductive tillers/plant was not affected in this study by the defoliation treatment because it was applied early in the growing season, when the vegetative apex started to differentiate into reproductive. Seed production was also not affected per plant very likely because they had enough time to recover their foliage and could supply sufficient resources to seed production.